The present invention relates to rotor cooling and, more particularly, to a rotor cooling circuit including combined compressor cooling and turbine cooling to thereby increase efficiency and total power output.
In a gas turbine, the unit rotor during its full load operation experiences temperatures higher than the material capability. As such, the rotor components are subject to low cycle fatigue (LCF), embrittlement and creep issues, which are detrimental to the performance of the system. The unit rotor wheels require a positive purge system to cool the wheels during full load operation. The rotor purge also maintains uniform wheel temperatures during startup and shutdown to achieve good wheel to wheel behavior.
Typically, the unit rotor receives cooled cooling air (CCA) through the compressor discharge casing (CDC) and the inner barrel. This flow is channeled from the aft end of the compressor cavity, down through the air-tubes in the distance piece into the centerline of the unit rotor. The cooling flow is split at the bore section forward for the compressor rotor cooling and aft for the turbine rotor cooling. The amount of flow going to each circuit is controlled at the flange or the rabbet joints through design features such as metering slots. See FIG. 1.
This cooling scheme uses an excess amount of CCA, which impacts the overall efficiency of the machine and the final power output. Additionally, the greater amount of cooling flow requires a larger size heat exchanger, which also results in an efficiency loss in the overall scheme of the system.
It would be desirable to improve the efficiency and power output of the overall system by modifying the CCA rotor-cooling scheme.